The present invention relates to magnetic disk drives. In particular, the invention relates to a magnetic disk drive which supports servo sectors each having a servo sector number section in which servo sector number information, shorter than the bits required to express the servo sector number itself, is written.
Recently, due to the demand for larger capacity magnetic disk drives, it has become necessary to raise the data space's share of the disk format as well as to raise TPI (Track Per Inch) and BPI (Bits Per Inch). On a disk, there are a large number of concentric tracks each having data sectors for user information and servo sectors for servo information used to locate the head to the track.
As described in Patent Document 1 (U.S. Pat. No. 5,903,410) and Patent Document 2 (Japanese Patent Laid-Open No. 6-243590), a typical magnetic disk drive nowadays employs such a format that from each data sector, the conventional ID section containing information to determine the logical address of the data sector is omitted so as to raise the data sector's share. In the format described in Patent Document 3 (U.S. Pat. No. 6,288,861), the servo sector number section is omitted from the servo sector so as to further reduce the servo sector's share.